Power Surge

Hydro-electricity – Creating Electricity from Water. We asked Edison Mission Energy to lead us around the Dinorwig and Ffestiniog Power stations in Wales.

The Answer is in the Mountains

Edison Mission Energy is one of the world’s leading independent power producers. We own and manage a portfolio of power projects around the globe which together can generate many thousands of megawatts of electricity. Edison Mission Energy is one of four businesses within the Edison International group, itself a recognised world leader in electricity generation, research and technology, financing and marketing. Edison Mission Energy owns and operates Dinorwig and Ffestiniog Power Stations in North Wales.

Dinorwig Power Station
Located close to the picturesque and protected Snowdonia National Park, the natural topography of the area provides an ideal location for pumped storage production. Despite the enormous scale of the construction project, there is very little visual evidence that a unique engineering achievement exists within the locality.

The original underground construction work involved the removal of 3 million tonnes of slate, silt, stone and grit. In total 12 million tonnes of material were excavated. What is remarkable about Dinorwig is that virtually all the tunnels, pipes and generation plant are located inside Elidir Mountain, thanks to one of the largest and most complex civil engineering projects that the UK has ever witnessed. To preserve the magnificent views looking south towards the Snowdon range, Afon-y-Bala dam on the north shore of Llyn Peris was constructed to a height of only 4 metres, not nine as originally planned. Moreover, the bed of Llyn Peris was re-shaped to avoid silt build-up, plant erosion or flood water draining into local rivers.

The environment has been improved through a range of initiatives, particularly the clearing of unsightly residues from Elidir Mountain, a legacy of Dinorwig’s past slate industry. Llyn Peris was also restored to its original state during construction as excessive slate extraction in the late 18th century had caused a build-up on the lake’s perimeters, creating disfigurement of the Dinorwig landscape.

Ffestiniog Power Station
EME also owns and operates Ffestiniog Power Station situated on the boundary of the Snowdonia National Park amongst some of the most breathtaking and inspiring scenery in the UK.

The cwms and ridges formed during the last ice age have added to the majesty and natural beauty of the area. Stwlan reservoir was constructed in a cwm 503 metres above sea level in the Moelwyn mountains.

The famous Ffestiniog narrow gauge railway still runs along the valley, having first operated as a slate-carrying service in 1836. After 1900, the trade in slate gradually declined and the line finally closed in 1946.

Both power stations are located within Landscapes of Historic Interest in Wales, (Countryside Council for Wales). They are important and significant historic landscapes.

Dinorwig Hydraulic System – Pumped Storage Electricity Generation
Pumped storage hydro-electricity works on a simple principle. It requires two reservoirs at different altitudes and is essentially a closed loop system as indicated in the diagram below.

Dinorwig power station is capable of producing 1728 MW of electricity from six, 288MW generators. Dinorwig’s six reversible pump/turbines are capable of achieving maximum output, from zero (standstill) within 90 seconds. The storage capacity of Dinorwig can produce 9100MWh of electricity, which is equivalent to 5 hours electricity at full load.

Up to 7 million cubic metres of water are stored in Marchlyn Mawr (Dinorwig’s upper reservoir). When the instruction is issued to start generation, the water is released through the headgates into a concrete-lined low pressure tunnel system. As the down-flow reaches the surge shaft it then plummets some 568 metres (eleven times the height of Nelson’s Column) before entering the high pressure tunnel system.

This splits into six separate and narrower steel-lined penstocks which direct the water through massive inlet valves and into the turbines. Each turbine is connected to its own generator and as the shaft of the turbine spins, it rotates the generator’s huge central rotor which spins within a stator to produce electricity. The generated electricity is then boosted to 400,000 volts by the transformer network, before connection to two sets of 400kV cables which transmit the electricity 11 kilometres underground to nearby Pentir substation. From here it is fed into the grid system.

After the water has passed through the power station, it is collected in Llyn Peris (the lower reservoir), passing through three tailrace tunnels which lead to tailgates that open into the reservoir. The water is then pumped back to Marchlyn Mawr (usually overnight) by using the generator as a motor to reverse Dinorwig’s turbines to act as pumps, which return the water back to refill the upper reservoir through the same system of tunnels and shafts.

There are four steps:

• Stage 1 – Storage: Water is stored in a reservoir near the top of a mountain
• Stage 2 – Release: When electricity is required a valve opens in the power station, this connects to the top reservoir and water rushes down large pipes to the turbines. The amount of water released depends on the amount of electricity needed.
• Stage 3 – Generation: The energy in the water is used to drive turbines. The turbines power generators to create electricity. Once the energy is removed from the water, another valve is opened and the water is discharged into the lower lake. The electricity produced is transported along power lines to the National Grid system and finally to our homes and businesses.
• Stage 4 – Pumping: To close the loop, the water in the lower reservoir must be returned to the upper reservoir. The process is reversed and the generators are used as motors to reverse the turbines and pump the water back to the top of the mountain.

Edison Mission have donated two family tickets for each of Ffestiniog and Dinorwig power stations. They can be claimed using gug reward points. See the gug rewards area for details.

For more information:
www.fhc.co.uk
www.edisonpowerprogramme.com

Please note that Edison Mission do NOT give permission to reproduce material or images from this article.

Sue McClaren - Edison Mission - 01/08/04

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